But December and January saw the worst outbreak of violence in the region since the end of the Troubles, Northern Ireland's 30-year conflict. Unlike that turbulent period, though, this latest spate of on-and-off rioting isn't between Northern Irish security forces and traditionally Catholic republicans seeking to unite the North with the Republic of Ireland – the old dynamic that largely ended with the 1998 Good Friday Agreement. Nor is it a result of clashes between republicans and pro-British, Protestant unionists – another frequent theme of the Troubles. Both factions now share power in Stormont, Northern Ireland's political assembly.

Rather, the current violence is being committed by unionists and directed at Stormont itself. After a Dec. 3 vote by the Belfast City Council to fly Britain's Union Jack flag on 17 designated days, rather than year-round, violence broke out immediately as enraged unionists stormed City Hall, and continued, with a short break over Christmas, right into the new year.

The flag debate may have been the match, but the flames are fueled by something much deeper. While Northern Ireland remains part of the United Kingdom, and is now constitutionally guaranteed to do so until the populace votes otherwise, unionism appears to be fracturing along class lines. That leaves its urban, working-class members – "loyalists" who have made up the rioters – increasingly brittle and disconnected from unionism's leaders, something that may portend an unsettled future if loyalist heckling grows into sustained violence or even a new "refusenik" political movement that rejects the peace process.

A changed world

There are at least three post-conflict narratives at work in Northern Irish society. The first is one of a shared future with "parity of esteem" for the British and Irish traditions. The second is of the inexorable march toward a united Ireland, in which the peace accord was a mere stepping-stone. The third says that Northern Ireland is, as former British Prime Minister Margaret Thatcher once put it, "as British as Finchley."

No one of the three has achieved dominance over the rest. The pro-British Democratic Unionist Party (DUP), once a vitriolic fringe organization, governs Northern Ireland's power-sharing assembly along with Irish republican Sinn Féin, the former political wing of the Irish Republican Army.

But while the peace process brought about a precarious status quo, members of the loyalist communities feel they are its forgotten victims.

Traditional manufacturing industries that employed tens of thousands have declined since the 1960s, leaving loyalists attached primarily to expressions of British culture, such as parades, to commemorate historical military victories. Meanwhile, the shift away from overtly British emblems like the Belfast City Hall flag, viewed as contentious and divisive by republicans and liberals alike, has fueled a unionist sense of victimhood. While equally economically deprived republicans are upbeat and view power-sharing and equality as hard-won victories, a sense of gloom pervades loyalist areas, and the vote to restrict flying the flag was seen by many as an assault on Britishness.

Feeling abandoned

The flag protesters, both peaceful and riotous, demonstrate one thing clearly: a political disconnect between unionism's leaders and its foot soldiers.

"It certainly shows a dislocation between the leadership of the DUP and the people," says Willie Frazer, a leader of the flag protests whose recently convened Ulster People's Forum has become the public face of unionist anger.

Mr. Frazer's lament is a common one among working-class unionists, but blame is spread around. Class divisions within unionism and estrangement from Britain often rise to the top of the list of complaints.

On Facebook and Twitter, loyalist thinking – and anger – can, for the first time, be observed by outsiders. Paul Reilly, a lecturer in media studies at the University of Leicester in England, has been studying the riots through the prism of social media.

"Facebook in particular has clearly provided a space for people dissenting from the main unionist parties, who are angry at them for going into government with Sinn Féin," he says. "There's a perception that equality has meant a loss. It's about a broader dislocation from Stormont and the peace process."

"You can't have a constant chipping-away [at British identity]. It has to be shared and talked through. Sinn Féin has embraced all of its people, including those who went to jail. But middle-class unionism has left the working class, and people who went to jail, behind."

Raymond Spiers, a veteran leader of the Orange Order, a Protestant fraternal organization, puts it even more robustly.

"After 30 years of a violent republican campaign, they [Sinn Féin] changed strategy and moved into the democratic process and continued with a culture war — a 'de-Britification' of Northern Ireland.

"The stated aim of the republican movement is the reunification of Ireland. Our own British government, which is complicit, believe in helping Sinn Féin to achieve a united Ireland. They're not providing any support for us as British citizens," he says.

Frazer, who has called for the shutting down of the local Stormont assembly and a return to rule from London, says remaining in political union with Britain is not all there is to unionism.

"What is the union? If you erode everything you believe in, what's left?" he asks. "Sinn Féin is destroying our culture from within; they're taking our identity away. What use is a Rolls-Royce with no engine or gearbox? To us the union is more than simply saying we're part of something."

'Too narrow a unionism'

The disconnect cuts both ways, though. Middle-class unionists are as divorced from their working-class compatriots as vice versa.

Newton Emerson, a unionist newspaper columnist whose wry take on Northern Ireland's politics is popular among readers of every political stripe, says the numbers involved in the protests aren't significant.

"There will always be a minority of people who won't agree to anything. The 'Angry Prod' [Protestant] hyperdefensive phenomenon has really died out. There is now a general ambivalence, which is why this seemed to come out of left field," he says.

Mr. Emerson also disputes the claims of a culture war: "Your culture is your effortless day-to-day life. I honestly don't believe that most people in Northern Ireland spend their time thinking about the culture war. The idea that Sinn Féin is pushing every button to make unionism implode is implausible."

Trevor Ringland, who left unionism's other main party, the Ulster Unionist Party, to join the British Conservative Party, says unionism's obsession with flags, emblems, and religion has come back to bite it.

"In some ways, we've allowed too narrow a definition of unionism to be seen by the wider world. The narrow type of Ulster unionism represented by the likes of Ian Paisley and the more right-wing political parties has hit its limitations in terms of who it can represent." (Mr. Paisley is a firebrand and cofounder of the DUP.)

He also says the protesters are further damaging their cause: "You don't promote remaining part of the United Kingdom by doing this."

"There are 125,000 Protestants in Belfast. How many are out on the streets?" he asks. "It's the usual rent-a-crowd of people who don't leave their own areas."

Nonetheless, says Dr. Shirlow, the sense of grievance is not entirely without merit.

"One of the things they say that is fair is that they are misunderstood. Every section of society laughs at them and lampoons them. They understand they've been cut adrift by middle-class unionist politics," he says.

A real anger

As January comes to an end, Belfast is much calmer than before, with trouble being sporadic in nature and localized to the east of the city.

But the anger on display from protesters remains real, however diminished their ranks. Standing outside the Methodist Church's East Belfast Mission building on Jan. 26 – where Northern Ireland's First Minister and DUP leader Peter Robinson was to meet with the local community – the mood at times descended into paranoia.

Protesters outside the building met Monitor requests for comment with a barrage of aggressive posturing and complaints about how the mission was secretly "funded" by Americans.

All they would say was: "We're here to see the glorious leader," sarcastically referring to Mr. Robinson.

It wasn't only the Monitor the protesters refused to speak to: They also refused to enter the mission to join the discussion, insisting Robinson come out and speak to them on the streets. The meeting went ahead without them.

Jim Wilson, a local loyalist community worker and former paramilitary who attended the meeting with Robinson, says it was useful (reporters were excluded). But his frustration that it has taken so long for the man who is the leader of Northern Ireland's government – and of unionism – to meet with loyalists was clear.

"Of course it has helped. It's his first time meeting them [the local residents]. There are more people in there [at the meeting] being constructive than there is [outside] being negative," he said.

Evidently not everyone shared his view. Outside, Mr. Wilson was later verbally abused by protesters, and his wife slandered.

A return to the Troubles?

Frazer, of the Ulster People's Forum, warns of a return to war: "If something isn't done, it could be 1969 all over again. In certain areas, they're using the [loyalist] paramilitaries to keep the foot on the neck of the people," he says.

Most think this prognosis is unlikely, but the nightmare scenario is renewed rioting in the run-up to the summer "marching season," when the Orange Order takes to the streets – in the case of some parades, much to the chagrin of republicans.

Annual rioting over the summer is commonplace, if not widespread, but fears of larger confrontations between loyalists and republicans bring back bad memories.

But where Frazer blames loyalist paramili-taries for crushing protest, others think the gun is in the other hand. The Police Service of Northern Ireland has repeatedly accused paramili-taries like the UVF of orchestrating violence.

Gerry Lynch, a former member of the cross community and softly pro-union Alliance Party, says the trouble is an indirect result of an attempt by the DUP to reclaim its former parliamentary seat in East Belfast, now held by the Alliance Party. When the DUP leafleted against the flag vote to boost its standing in East Belfast, the UVF saw the opportunity to use the issue toward its own ends – turning the flag issue into something more toxic.

"The DUP leaflets [demanding the flag vote be canceled] struck a nerve. It's a silly issue, but it struck a nerve with working-class Protestants," Mr. Lynch says. "Not all of loyalism has bought into this, but the temperature is very high. There are senior figures in the UVF on whom the [police's] Historical Enquiries Team is closing in. That's what this is really about."